Hydrocarbons in seawater and organisms and microbiological investigations : final report submitted to the Gulf Universities Research Consortium for the offshore ecology investigations

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[Part I:] A liquid-liquid extraction technique has been used to determine the amounts and distributions of n-paraffins and selected isoprenoid hydrocarbons in seawater collected from nearshore areas in the northeastern and central Gulf of Mexico. The dominant saturated hydrocarbons in seawater were n-paraffins with chain lengths from nC-15 to nC-41 as well as the isoprenoid hydrocarbons pristane and phytane. Concentrations of n-paraffins plus isoprenoids ranged from 0.03 to 0.60 [mu]g/l and were similar in value at nearshore study sites containing producing oil wells compared with "control" stations in the Gulf of Mexico displaced hundreds of miles from the study site. Seawater from Timbalier Bay generally contained higher concentrations of n-paraffins than the offshore samples and exhibited a more pronounced odd-even carbon preference in the range nC-25 to nC-33. This was attributed to the high load of particulate detritus presumably derived from terrestrial plants in Timbalier Bay water. Estimates of total saturated hydrocarbons in most samples were approximately 10 times larger than the concentrations of n-paraffins as determined by integration of the total paraffin signal.

[Part II:] A bacteriological survey carried out in conjunction with the OEI studies indicated that the percentage of hydrocarbon degrading microorganisms in the “total” population did not differ significantly between the OEI study areas (offshore Louisiana and in Timbalier Bay), and “Gulf” control stations several hundred miles away in non-oil production areas. It is hypothesized that the hydrocarbon concentrations in all water samples were too low to be reflected by a significant increase in the percentage of hydrocarbon degrading microorganisms. Thus the percentage values reported might be considered “baseline” data for the Gulf of Mexico.